Politics is tribal. When a candidate commits a typical gaffe, his opponents attack while his allies mount a defense. That’s just the way it goes. But once in a while, a candidate says something so devastatingly stupid everything gets turned around. A day after Missouri congressman Todd Akin told a local TV interviewer that victims of “legitimate rape” don’t get pregnant, national Republicans called for him to abandon his challenge to Senator Claire McCaskill while Democrats welcomed the chance to fight for the pivotal seat on more favorable ground.